1. Field of Inventions
The present inventions relate generally to the treatment of the heart and, more particularly to treatments that, among other things, stimulate angiogenesis and relieve angina.
2. Description of the Related Art
Atherosclerosis, which is a leading causes of death, occurs when plaque develops at various locations within the arterial system, thereby restricting the flow of blood through the affected vessels. When atherosclerosis occurs within the blood vessels that supply blood to the muscles of the heart, myocardial infarctions, ischemia and/or angina can result due to the reduction in blood flow.
A variety of myocardial revascularization techniques have been developed in recent years in an attempt to increase the flow of blood into the heart muscle and to stimulate angiogenesis, i.e. the creation of new blood vessels within the heart muscle. In percutaneous myocardial revascularization (PMR), which is also referred to as direct myocardial revascularization (DMR), channels are formed in the endocardial surface with catheter-based devices. The PMR and DMR channels extend partially through the ventricular wall. Transmyocardial revascularization (TMR), on the other hand, involves the formation of channels that extend completely through the ventricular wall. Although the use of mechanical piercing and cutting devices has been proposed, the revascularization channels are typically formed with a laser device or the combination of mechanical and laser devices. Radiofrequency energy delivered through an electrode has also been used to create craters on the endocardial surface.
Although they have proven to be useful, the inventor herein has determined that there are a number of shortcomings associated with conventional myocardial revascularization techniques. For example, the creation of channels through the ventricular wall during TMR is a relatively time consuming procedure and additional time is required to stop the bleeding associated with the procedure. A single channel takes about three to five seconds to create and pressure must be applied to the channel (usually with a finger) for one to two minutes in order to give the blood time to clot and stop the bleeding. The TMR procedure also requires a relatively invasive muscle-sparing thoracotomy to access the heart and results in measurable blood loss (typically about 200-300 cc). Moreover, the pulse or continuous wave energy applied to the tissue during laser-based PMR, DMR or TMR can entrain the patient""s heart rhythm and cause fibrillation or tachycardia.
Cardiac denervation, which provides relief from angina pain, is a beneficial side effect of the aforementioned myocardial revascularization techniques. Patients experience pain relief because some of the nervous tissue in the ventricular wall is destroyed during the channel formation process. The present inventor has, however, determined that the level of cardiac denervation achieved by conventional myocardial revascularization techniques is susceptible to improvement. For example, the cross-sectional area of the channels is relatively small, which limits the volume of nervous tissue that is destroyed by the channels. PMR and DMR techniques are further hampered by the fact that the nervous tissue is concentrated close to the epicardial surface. PMR and DMR channels, which extend through the endocardial surface and only partially through the ventricular wall, fail to reach the region closer to the epicardial surface that contains the higher concentration of nervous tissue.
Accordingly, the general object of the present inventions is to provide methods and apparatus that avoid, for practical purposes, the aforementioned problems. In particular, one object of the present inventions is to provide methods and apparatus for stimulating angiogenesis that can be performed more quickly, and with less bleeding, than conventional PMR, DMR and TMR techniques. Another object of the present inventions is to provide methods and apparatus for stimulating angiogenesis that will not cause fibrillation or tachycardia. Still another object of the present inventions is to provide methods and apparatus for myocardial revascularization that destroy larger volumes of nervous tissue than conventional PMR, DMR and TMR techniques.
In order to accomplish some of these and other objectives, a myocardial treatment method in accordance with one embodiment of a present invention includes the steps of positioning an electrode on the epicardial surface of a ventricle and transmitting energy from the electrode, through the epicardial surface and into the ventricular wall to create a lesion within the ventricular wall. With respect to apparatus, an apparatus in accordance with one embodiment of a present invention includes a shaft and one or more electrodes that have a main portion and a needle portion. The electrode main and needle portions are constructed and arranged relative to one another such that the electrode main portion will rest on the surface of a body structure, such as a ventricle, when the electrode needle portion penetrates the body structure.
There are a number of advantages associated with the present methods and apparatus. In the area of myocardial revascularization, for example, the present surgical probe may be used in a procedure in accordance with the present method to form a lesion with a relatively large portion at and near the epicardial surface. The electrode needle portion may be used to form a relatively small lesion portion below the relatively large portion. Preferably, the needle portion is movable, which allows the physician to selectively alter its depth to achieve the desired levels of additional lesion formation. The thermally damaged area (i.e. the area in which the lesion is formed) will stimulate angiogenesis. In contrast to PMR, DMR and TMR procedures, which require time consuming channel formation, a suitable epicardial lesion pattern may be created quickly. A lesion creation procedure in which, for example, 20 lesions are created will typically take about 10 minutes to complete, as compared to 30 minutes for typical PMR and DMR procedures where 20 channels are created and 60 minutes for a typical TMR procedure where 20 channels are created. The formation of epicardial lesions is also superior to PMR, DMR and TMR procedures because it does not cause the bleeding that occurs during channel formation.
The present methods and apparatus also destroy nervous tissue, and provide angina relief, in a manner that is more efficient than PMR, DMR and TMR procedures. As noted above, nervous tissue is concentrated near the epicardial surface. The formation of lesions that have a relatively large lesion portion at and near the epicardial surface will, therefore, result in far more cardiac denervation and angina relief than that which can realized through the formation of channels that have small cross-sectional areas and, in the case of PMR and DMR in particular, channels that do not reach the portion of ventricular wall with the higher concentrations of nervous tissue.
A preferred implementation of the present apparatus includes a relatively short shaft that facilitates use of the apparatus in thoracoscopic procedures. As such, the electrode (or electrodes) may be visually guided to the desired location on the epicardial surface. This is easier and less time consuming than manipulating the distal end of a relatively long endovascular catheter to position a channel or crater forming device on the endocardial surface, as is the case with PMR and DMR procedures. Thoracoscopic procedures are also less invasive than the muscle-sparing thoracotomy associated with TMR procedures.
The above described and many other features and attendant advantages of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.